Neuron specific enolase, NSE and non neuronal enolase, NNE are specific biochemical markers for neurons and glia respectively. The NSE is also present in neuroendocrine cells of the APUD classification. Clinical studies with small cell lung cancer, neuroblastoma and pancreatic islet cell tumor patients has shown that serum NSE levels can be used to detect these conditions as well as monitor the clinical course of illness. Basic studies have shown that NSE appears during development at precisely the time when synaptogenesis is occuring.